The objective of this work is development of a laser Doppler catheter system (LDCS) for the invasive assessment of vascular flow. Current noninvasive assessments of coronary flow (radionuclide imaging and radioactive microsphere distribution) are complex and expensive, while lacking resolution and clinical utility. LDCS would allow absolute subselective assessment of coronary flow and stenosis in individual arteries, and measurements could be obtained during diagnostic cardiac catheterization using standard techniques. The expected results of the Phase I effort will be to construct a prototype catheter system capable of measuring velocities up to 2 meters/second. The system will be calibrated in a hydraulic test loop, and will be used to measure arterial flow in dogs with simulated stenosis. Significance of the work: The LDCS would have widespread application in the physiologic assessment of coronary artery disease. Coronary angiography yields no physiologic information and often underestimates intermediate (25% to 60%) stenosis. Laser Doppler techniques, by sensing the high velocity flow region in the stenotic lumen, could aim high power therapeutic laser catheters. Perforation risks would be minimized and treatment effects could be monitored.